In a local area network (LAN) information is sent from workstation to workstation in the form of packets. Each packet contains a header and data portion. The header portion contains control type information such as destination address, source address, the type of information being transferred, and error correcting codes. The data portion contains the actual information to be transferred from one workstation to another.
Workstations are connected to each other over a medium such as wire cables or fiber optic cables. The cables usually lead from the individual workstations to a hub or concentrator. The plurality of workstations connected to a single concentrator is often known as a segment. A plurality of segments, each having their own concentrator, can be connected to each other by connecting the concentrators.
One of the simpler embodiments of a concentrator is provided with only a repeater function. Any packet that is received by a repeater from a workstation is sent out to all other workstations connected to the repeater. When a plurality of segments, each having repeaters, are connected to each other, a packet generated by one workstation is spread throughout the entire LAN. The destination address of the workstation to receive the packet is included in the header of the packet. Workstations that are not to receive the packet, disregard or ignore the packet.
As the number of segments and workstations increase on a LAN, the number of packets traversing the LAN, or the traffic, also increases. With all the workstations and segments connected by repeaters, the packets going to all workstations causes delays for the packets and a corresponding lowering of performance of the network.
Bridges and routers are known to connect segments and only transfer packets from one segment to another segment if the destination address of the packet is on the other segment. Otherwise a packet will not be delivered into a segment.
Routers are more sophisticated than bridges and can route packets according to additional conditions. Routers are also more complicated and more expensive than bridges or repeaters. Correspondingly, bridges are more complicated and more expensive than repeaters.
Very often it is desirable to provide individual groups of workstations within a single segment, or to have a single group encompass several segments. Also, it may be desirable to have several different groups each contain separate portions of several different segments. The routing of packets to only members of the same group can become very complicated and expensive if routers are used. Also very often a single workstation will send a multi-cast or broadcast packet intended for all members of its own group. With traditional bridges and routers, a broadcast packet would go to all members of all groups. This is not desirable since it needlessly increases traffic and may also be undesirable from a security view point.
Also when a workstation is moved, or a person wants to move to a different workstation and still receive their same information, reconfiguration of a router is very involved. The same is true when additional workstations must be added to a router's configuration, or a particular workstation wants to be associated with a different group of workstations on the LAN.